Combination catalytic cracking process

ABSTRACT

IN A SYSTEM WHEREIN A DIRTY OIL FLUID CATALYTIC CRACKING SYSTEM AND A CLEAN OIL CATALYTIC CRACKING SYSTEM ARE OPERATED, THE SLURRY OIL FORM THE DIRTY OIL UNIT IS, AT LEAST IN PART, CHARGED TO THE FRACTIONATOR FOR THE CLEAN OIL UNIT TO DILUTE THE CATALYST LOADING OF THE CLEAN OIL UNIT&#39;&#39;S SLURRY, WHICH MINIMIZES EROSION OF THE SLURRY PUMPS, INCREASES HEAVY CYCLE OIL PRODUCTION, AND DECREASES GAS AND COKE PRODUCTION.

J y 1971 R. c. MASON, JR

COMBINATION CATALYTIC CRACKING PROCESS Filed Sept. 10. 1969 2Sheets-Sheet 1 BY gm al ay R a m J Tl N 2 f NT 00 ECU f WIS VAN NCA OT w5 m R 7 8 3 3 l 2 r C 9 O Ilil'llll' p m 2 4 5 .w 2 3 I A fl 4 EOP ZOFUE ll 4 7 moQzoFQE m A 2 u 4 4 m N 2 m r. w f C M m L V C .l. M m f M W.O YK T Y N AA TU T E mm m mm a C D D E L mm A R m 5 Tc A G UNIT 27ATTORNEYS United States Patent O US. Cl. 208-78 4 Claims ABSTRACT OF THEDISCLOSURE In a system wherein a dirty oil fluid catalytic crackingsystem and a clean oil catalytic cracking system are operated, theslurry oil from the dirty oil unit is, at least in part, charged to thefractionator for the clean oil unit to dilute the catalyst loading ofthe clean oil units slurry, which minimizes erosion of the slurry pumps,increases heavy cycle oil production, and decreases gas and cokeproduction.

BACKGROUND OF THE INVENTION This invention relates to a catalyticprocess wherein hydrocarbons are catalytically converted to morevaluable products. In one aspect, this invention relates to amodification of a catalytic cracking operation wherein at least twocracking steps are conducted at substantially the same levels ofconversion and wherein the slurry oil removed from one step is passedalong with the reactor effluent from the other step to the samefractionation zone. In another aspect, the invention relates to a methodfor increasing the yield and improving the quality of products obtainedin a catalytic cracking operation, wherein the cracking steps areoperated substantially at the same levels of conversion. In stillanother aspect, the invention relates to a method and means fordecreasing coke and hydrogen production in a catalytic crackingoperation wherein the feed stream is contaminated with metal compoundssuch as nickel, vanadium, or iron.

The conversion of oils is well known. Also, the specific conditions forconverting virgin or cracked oils of various kinds are fairly Wellestablished in the art. There are known also certain combinations ofoperations, each of which is designed to produce certain advantages ofopera tions, yield, or product quality or a combination of one or moreof these related objects.

It is known to employ two or more cracking zones wherein feed stockscontaining differing concentrations of contaminating metals areseparately cracked. An improved process for operating a plurality ofcracking zones in the hydrocarbon conversion process has recently beenproposed wherein a relatively refractory highly parafiinic, lowmetal-content hydrocarbon is supplied to a first catalytic cracking zoneoperated at high conversion level; a less refractory, high metal-contenthydrocarbon feed is supplied to a second catalytic cracking zoneoperated at low conversion; and the heavy cycle oil and decant oil fromthe two cracking zones are solvent extracted to provide a raffinatestream which is passed as a portion of the feed stock to the firstcatalytic cracking zone. The aromatic oil from the solvent extractionstep is valuable as a carbon black process feed stock.

This new method of operation has greatly increased the catalyst life inthe clean oil cracking step which is operated at high conversion levels;however, the clean oil charged to the clean oil unit did not provide thesufficient coke laydown on the catalyst to provide the required amountof heat in the regeneration step to operate the catalytic cracking unit.It was found that the heat requirements in the regeneration step of theclean oil unit could be met by passing a portion of the highest boilingfraction of the low level conversion catalytic cracking unit to theclean oil unit so as to provide a coke laydown on the clean catalystwhich will be sufiicient to supply the necessary heat to operate theclean oil units satisfactorily.

It has now been found that an improved operation occurs when thecracking steps are conducted at substantially the same levels ofconversion when, at least, a portion of the slurry oil recovered fromthe dirty oil cracking zone effluent is charged along with the clean oilcracking zone eflluent to the same fractionation zone. The newoperation, according to the invention, produces additional heavy cycleoil instead of low value gas and coke produced in the conventionaloperation which additional heavy cycle oil allows production of about10,000 pounds of additional carbon black per day.

Accordingly, the object of this invention is to provide a method forimproving the qualit and quantity of products obtained in a catalyticcracking operation employing a plurality of cracking steps.

It is also an object of this invtntion to provide a method of operatinga cracking operation employing a plurality of cracking steps so as todecrease the amount of coke and hydrogen produced.

Still another object of this invention is to provide a method foroperating a catalytic cracking process employing a plurality of crackingsteps so as to increase production of heavy cycle oil with a resultantincrease in the production of carbon black.

Another object of this invention is to provide a method for operating acatalytic cracking process employing a plurality of cracking steps so asto decrease the reboiler heat load on the clean oil fractionation zone.

Other objects and advantages will be apparent to one skilled in the artupon study of this disclosure including the detailed description of theinvention and the appended drawings.

STATEMENT OF THE INVENTION According to the present invention, at leasta portion of the highest boiling fraction (slurry oil) of the dirty oilcatalytic cracking unit recovered as the bottoms product in thefractional distillation of the catalytic cracking step efiluent ispassed to the clean oil fractionation zone along with the effluent fromthe clean oil catalytic cracking unit so as to increase production ofheavy cycle oil and decrease the amount of low value gas and cokeproduced.

In accordance with one embodiment of the invention, a substantialportion of the total bottoms product recovered as the fractionatorbottoms from the dirty oil catalytic cracking unit is charged to theclean oil catalytic cracking zone fractionator below the vapor feedthereto. When desired, all of the total bottoms product recovered asfractionator bottoms from the dirty oil unit is charged to the clean oilfractionator. In some instances, however, it is preferable to recycle atleast a portion of the total bottoms product recovered as thefractionator bottoms from the dirty oil unit to the dirty oil crackingzone reactor and pass the remainder to the clean oil fractionation zone.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a diagrammatic flowplan of one embodiment of the invention.

FIG. 2 is a diagrammatic flow plan of a specific preferred embodiment ofthe invention.

Referring now to FIG. 1, a hydrocarbon feed stream is fed to catalyticcracking zone 10 by way of line 11.

The feed stream introduced by way of line 11 is made up of gas oil andother distillates so that the metal content of the feed stream is quitesmall. The recycle streams which can be introduced by way of lines 12and 13 make up the total feed to the catalytic cracking zone 10. Aheater (not shown) heats the fresh feed and recycle streams to atemperature slightly under that at which thermal cracking might occurprior to admission to the cracking zone 10. Hot regenerated catalyst isadded to the catalytic cracking zone by way of line 14 and used catalystis removed by way of line 15 and passed to a regeneration zone (notshown) and is then returned to the catalytic cracking zone 10 at atemperature higher than the catalytic cracking temperature so that themixture of heated oil and regenerated catalyst achieves the desiredcracking temperature in the cracking zone' The catalyst can be anydesired type cracking catalyst and in the embodiment of the inventionbeing described the catalyst is a silica-alumina cracking catalyst.Also, in the embodiment of the invention presently described, thecatalytic cracking reactors are of the fluidized flow employing a finelydivided catalyst, a regenerator also employing the fluid-solids flowtechnique, along with fractionating facilities and other facilities makeup the system known in the art as an FCC unit.

The hydrocarbon effluent from catalytic cracking zone 10 is passedthrough line 16 to the product fractionator 17 wherein the effluentproducts are separated into fractions having diflierent boiling rangesfrom whence C and lighter materials are removed by way of line 18, agasoline cut is removed by way of 19, and light cycle oil is removed byway of line 20 to form the various products of the process. Heavy cycleoil is removed by way of line 21 and passed to a solvent-extractionplant 22. The rate of withdrawal of heavy cycle oil in line 21 iscontrolled by liquid level controller 23 which measures liquid level inthe bottom of fractionator 17 which liquid level controller adjusts theopening of control valve 24. Total bottoms product including catalystfines carried over from catalytic cracking unit 10 by way of line 16 isremoved from the base of fractionator 17 by way of line 25, passedthrough pump 26, and at least a portion of the slurry oil removed asbottoms is passed by way line 13 to clean oil cracking unit 10 asrecycle.

A portion of the slurry oil removed by way of line 25 is passed throughcooler 27 and reintroduced into fractionator 17 by way of line 28. Thereis no decant oil produced by fractionator 17.

A conventional solvent-extraction process is employed in zone 22utilizing liquid sulfur dioxide as the solvent to extract aromatichydrocarbons. The aromatic compounds are absorbed from the oil so as toproduce a paraflinic raflinate which can be returned to the crackingzone 10 by way of line 12. Any suitable solvent can be utilized toextract aromatics from the oil. An aromaticcontaining extract oil isremoved from zone 22 by way of line 29 for use as feed for a carbonblack producing system.

A second hydrocarbon feed stream comprising topped crude, pitch, andother hydrocarbon fluids containing relatively large amounts of metalcontaminants or coke and gas forming components is fed to a secondcatalytic cracking zone 30 by way of line 31. Heat is provided to thefeed stream by means of a heater (not shown). Hot regenerated catalystand make-up catalyst for catalytic cracking zone 30 are introduced byway of line 32, and used catalyst is removed and passed to aregeneration zone (not shown) by way of line 33, or discarded ifdesired. Reaction efiluent from catalytic cracking zone 30 is passed byway of line 34 to a second product fractionator 35. C and lighterhydrocarbons are removed from zone 35 by way of line 36, a gasolinefraction is removed by way of line 37, and a light cycle oil is removedby way of line 38. Heavy cycle oil is removed by way of line 39 andpassed to a solvent-extraction zone 22 4 along with the heavy cycle oilin line 21. As indicated above, the aromatic hydrocarbon product whichcomprises the extract from solvent-extraction zone 22 is recovered byline 29 for use as a feed to a carbon black producing plant (not shown)or for other desired use.

In accordance with the invention, the total bottoms product fromfractionator 35 or slurry oil is removed by way of line 40, passedthrough pump 41, and all, or a substantial portion of the total bottomsoil net product can be passed by way of line 42 and introduced into alower portion or" fractionator 17. The slurry oil passed by way of line42 introduced into a lower portion of fractionator 17 is introduced at apoint below the vapor feed removed from catalytic cracker 10 by way ofline 16. If desired, a portion of the slurry oil removed from the baseof fractionator 35 can be passed by way of line 4-3 as recycle tocatalytic cracking unit 30.

Catalytic cracking zone 10 and 30 can be operated at different orsubstantially the same conversion levels and at different orsubstantially the same temperature. Ordinarily each of the zones will beoperated at a temperature in the range 805-970 F. The conversion levelin each zone can vary from about 30 to percent, preferably about 50percent for each zone.

The dirty oil will often be operated at a temperature 870960 F. and aconversion of 30-60 percent, whereas the clean oil unit will often beoperated at a temperature in the range 905970 F. at a conversion levelin the range 50-80 percent.

The amount of slurry oil passed from the dirty oil fractionator to theclean oil frationator will ordinarily be such that the amount ofcatalyst per gallon of oil the slurry removed from the clean oil unitdoes not exceed 0.5 pound of catalyst per gallon of oil. As indicatedabove, the total bottoms make from the dirty oil frationator, i.e., allof the slurry oil, can be passed to the clean oil fractionator. If,however, the amount of catalyst in the slurry oil removed from the cleanoil fractionator unit exceeds the maximum amount (about 0.5 gallon)desired then a portion of the total bottoms from the dirty oilfractionator can be recycled to the dirty oil cracking unit.

FIG. 2 illustrates a specific example of the operation of the inventionand demonstrates the advantages obtained by operating according to theinvention. There will be noted that operating conditions, i.e.,temperature for the dirty oil unit and the clean oil unit, according tothe invention are the same, whereas in the prior operation the dirty oilunit is generally operated at a somewhat lower temperature than theclean oil unit. The operation illustrated in FIG. 2 shows the fiow ofslurry oil from the dirty oil fractionator being passed to thefractionator following the clean oil unit or if desired some can bereturned to the dirty oil cracking unit. In the prior method, the slurryoil recovered from the dirty oil fractionator was passed as part of afeed to the clean catalytic cracking oil unit.

Operation according to the invention produces additional heavy cycle oilinstead of low value gas and coke produced in the conventionaloperation. In the specific example, the invention gains some $300 to$400 per day in oil product value. The additional heavy cycle oil isextracted to produce aromatic oil for carbon black manufacture. Aboutbarrels per day additional heavy cycle oil will allow production ofabout 10,000 pounds carbon black.

Also, less slurry recycle to the clean unit fractionator is required byusing the invention. This decreases the cooler heat load since lesscooling is required with the less recycle. The addition of slurry oil tothe clean oil fractionator cuts down the heat load and, hence, theamount of recycle slurry required.

The above advantages are illustrated in the following table wherein dataobtained from prior operation are compared with data obtained fromoperating according to the invention.

COMPARATIVE DATA Old Way Invention Topped crude cracking:

Charge, b./d 27,000 27, 000 Cracking temp.:

F 940 940 Range, F 870-960 870-960 Conversion:

Percent 50 50 Range, percent". 30-60 3060 Topped crude unitfractionator:

Bottom temp., F 670 670 Bottom press, p.s.i.g l l5 Slurry oil, b./d 4,000 4, 000 0. 02 0. 02 Gas oil cracking:

' 28,000 28, 000 4, 000 None 5, 000 5, 000 Catalyst, lb./ga.l 0. 478 0.497 Cracking temp.:

940 940 Range, F... 905-970 90 970 Conversion:

Percent... 60 60 Range, percent 5080 50-80 Clean oil unit fractionation:

Slurry from dirty unit, b./d None 4, 000 Catalyst, lb./gal 0. 02 Slurryreflux, b./d 72, 000 64, 800 Catalyst, 1b./gal 0. 478 0. 497 Heavy cycleoil yield, to /d 12, 000 12, 120 Slurry to reactor, b./d 5, 000 5, 000Catalyst, lb./gal 0. 478 0. 497

The quantity of catalyst fines contained in the slurry oil removed fromthe dirty oil fractionator depends, in part, upon the quantity of thisslurry oil which is recycled to the dirty oil cracking unit. Preferablynone of this slurry oil is recycled to the dirty oil cracking unit (andit contains, thusly, about 0.02 pound of catalyst per gallon). Theslurry oil from the dirty oil fractionator is substantiallymetal-contaminant-free and, preferably, is all charged to the clean oilfractionator in accordance with the invention. This is done so that thatamount of slurry oil (removed from the dirty oil fractionator) that isrecovered in the slurry oil removed from the clean oil fractionator willbe cracked in the clean oil catalytic cracking zone wherein the catalystcontains a relatively low amount of metal contaminants, resulting inless coke and gas production therefrom. The total slurry oil recoveredfrom the clean oil fractionator is recycled to extinction in the cleanoil catalytic cracking zone. It is this recycle operation, in part,which causes a build-up in the catalyst level in the slurry oil, and theslurry pumps presently used cannot properly handle oils having more thanabout 0.5 pound of catalyst per gallon due to erosion, etc.

The low catalyst content slurry oil from the dirty oil fractionator iscooler than the vapor charged from the clean oil cracker to the cleanoil fractionator. The addition of this cooler slurry oil from the dirtyoil fractionator to the clean oil fractionator allows the use of lessrecycle of cooled slurry oil from the clean oil fractionator back to theclean oil fractionator, and therefore there is less load on the bottomscooler of the clean oil fractionator. However, the slurry oil from thedirty oil fractionator does add a small portion of catalyst fines to theclean oil fractionator, which fines are also removed from the bottomthereof in the slurry oil. Since the slurry oil charged from the cleanoil fractionator to the clean oil cracker is the same in the prioroperation as in the invention, the solids content of the slurry oil fromthe clean oil fractionator is slightly increased when operating inaccordance with the invention. It can be seen that charging too muchslurry oil from the dirty oil fractionator to. the clean oilfractionator can bring the catalyst level up to an amount above themaximum allowable.

I-claim:

1. An improved process for catalytically converting hydrocarbon fluidsto valuable products which comprises:

(a) passing a gas oil stream having a low metal contaminant content to afirst catalytic cracking zone wherein said stream is subjected tocatalytic cracking,

(b) passing the eflluent obtained in step (a) to a first fractionationzone wherein the cracked products are separated into separate distillatefractions comprising light hydrocarbons, gasoline, cycle oils, and acatalyst-containing bottoms product,

(c) returning at least a portion of said bottoms product to said firstfractionation zone and recycling the remainder to said first catalyticcracking zone,

(d) passing a topped crude stream having a high metal contaminantcontent to a second catalytic cracking zone wherein said stream issubjected to catalytic cracking,

(e) passing the effluent obtained from step (d) to a secondfractionation zone wherein the cracked products are separated intoseparate distillate fractions comprising light hydrocarbons, gasoline,cycle oils, and a catalyst containing bottoms product, and

(f) passing at least a portion of said bottoms product obtained in step(e) to said first fractionation zone along with efiluent from said firstcatalytic cracking zone as feed for said first said fractionation zone,the amount of said bottoms product passed to said first fractionationzone being sufficient to increase the heavy cycle oil yield from thatfirst fractionation zone but insufficient to increase the ratio ofcatalyst to oil in excess of 0.5 pound of catalyst per gallon of oilremoved from the bottom of said first fractionation zone and returned tosaid first catalytic crackingzone.

2. A process according to claim 1 wherein the first catalytic crackingstep is conducted at a temperature in the range 905-970 F. and aconversion level in the range of about 50-80 percent, and the secondcatalytic cracking step is conducted at a temperature in the range of870960 F. and a conversion level of about 30-60 percent conversion.

3. A process according to claim 1 further comprising:

(g) passing the heavy cycle oils obtained from said first and secondfractionation zones to a solvent extraction zone wherein the oils areseparated into an aromatics-containing extract phase, and into aparaffin-containing rafiinate phase, and

(h) passing at least a portion of said rafiinate phase to said firstcatalyst cracking zone.

4. A process according to claim 1 wherein all of the catalyst containingbottoms product obtained from said second fractionation zone is passedto a lower portion of said first fractionation zone and is introducedbelow the vapor feed comprising the eflluent from said first catalyticcracking zone to said first fractionation zone, and further wherein bothof said catalytic cracking steps are carried out at about the sametemperature and about the same conversion level.

References Cited UNITED STATES PATENTS 1/1965 Mitchell 20878 6/1965Daniel et al. 20878 US. Cl. X.R. 20880

